1. Field of the Invention
The invention is directed to an improved injector for a common rail fuel injection system for internal combustion engines, having an injection nozzle at has a nozzle needle and having a control chamber, subdivided into three portions by a control plunger, wherein the first portion and second portion communicate hydraulically via an inlet throttle disposed in the control plunger, and the second portion is hydraulically in communication with a high-pressure connection and the third portion is hydraulically in communication with an inlet conduit to the nozzle needle, and the control plunger has two grooves, and between the grooves the control plunger is embodied as a slide and with a control edge of the guide bore, when the injection nozzle is closed, effects an extensive hydraulic separation between the high-pressure connection and the inlet conduit to the nozzle needle, and the stroke of the nozzle needle and the stroke of the control plunger are coupled with one another.
2. Description of the Prior Art
An injector of the type described above is described in German Patent Disclosure DE 199 63 920 A1.
The object of the invention is to further improve the injector known from German Patent Disclosure DE 199 63 920 A1, and in particular to expand the design possibilities for the course of the preinjection, main injection, and optionally post injection, such that overall, improved fuel consumption and emissions of the engine are obtained.
In an injector for a common rail fuel injection system for internal combustion engines, having an injection nozzle that has a nozzle needle, and having a control chamber subdivided into three portions by a control plunger, wherein the first portion and second portion communicate hydraulically via an inlet throttle disposed in the control plunger, and the second portion is hydraulically in communication with a high-pressure connection and the third portion is hydraulically in communication with an inlet conduit to the nozzle needle, and the control plunger has two grooves, and between the grooves the control plunger is embodied as a slide and with a control edge of the guide bore, when the injection nozzle is closed, effects an extensive hydraulic separation between the high-pressure connection and the inlet conduit to the nozzle needle, and the stroke of the nozzle needle and the stroke of the control plunger are coupled with one another, this object is attained in that a hydraulic connection that is closable by a multi-port directional-control valve is provided between the high-pressure connection, or the second portion, and the inlet conduit to the nozzle needle.
It has been found that by means of the additional hydraulic connection of the invention, which can be opened and closed by a multi-port directional-control valve, the injection into the combustion chamber can be accomplished in a simple way with the full rail pressure, without having to accept disadvantages in the shaping of the injection course of the preinjection and/or at the onset of the main injection. The requirements in terms of tightness and speed made of the multi-port directional-control valve required for this are not stringent, and so the costs for this multi-port directional-control valve are low. With the aid of the hydraulic connection of the invention, a postinjection at high injection pressure can also be accomplished, which has proved to be advantageous in reducing so-called black smoke in the exhaust gases.
In a variant of the invention, it is provided that the control plunger is disposed axially displaceably in a guide bore; that the nozzle needle is disposed axially displaceably in a bore extending coaxially to the guide bore; and that the coupling of the control plunger and nozzle needle is effected via a valve plunger. Because of the coaxial disposition of the control plunger and nozzle needle, the coupling forces can be transmitted directly and in a simple way. If necessary, the distance between the control plunger and the nozzle needle can be bridged with the aid of a valve plunger.
In a further expansion of the invention, the valve plunger and the control plunger, or the nozzle needle and the control plunger, are embodied integrally, thus reducing the number of components and avoiding errors of alignment.
For the purposes of the invention, it is advantageous if the multi-port directional-control valve is embodied as an electrically actuated 2/2-port directional-control valve, and in particular as an electrically actuated slide valve, since such valves are adequate in terms of their response and tightness and are simple to produce.
The reliability of the injector is enhanced if the multi-port directional-control valve is closed when without current.
In another variant, it is provided that a closing spring that is braced against the housing of the injector and against the nozzle needle is present, so that even in the absence of fuel pressure, the injector will always be securely closed. Moreover, the closing spring can contribute to the automatic re-closure, reinforcing the hydraulic closing force, once the magnet valve has been triggered a single time.
In a further feature of the invention, the hydraulic separation of the high-pressure connection and the inlet conduit to the nozzle needle is defined structurally by means of the overlap of the slide and the control plunger and by means of the fit between the slide and the guide bore, so that in tuning the injector, a further degree of freedom can be exploited.
Finally, it can be provided that an auxiliary spring acting on the control plunger is present, and/or that the inlet conduit to the nozzle needle, in conjunction with the fuel located in it, serves as a pressure reservoir, so that particularly in the main injection, it is assured that the control plunger will execute such a long stroke that there is no longer any overlap between the slide and the control edge, and thus the injection nozzle of the injector is subjected to the full pressure of the fuel. This enables fast opening of the injection nozzle, and a large quantity of fuel can be injected quickly.